anyone know if there's really any difference between the chipsets? i mean is one significantly better than the other, in terms of performance, data accuracy etc., reliability?
Yes, there sure is. I have a bytecc combo drive with the prolific PL3507 (rev. C), and it only works reliably when connected via USB2. The firewire connection does not work, period. Generally, I get delayed write failures, and ultimately corruption of the MFT. I have tried several firmware updates, but no luck yet.
If you plan on using firewire, stay away form this chipset. Do a Google search, and you will learn more about the issues with it.